The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, such scaling down has also been accompanied by increased complexity in design and manufacturing of devices incorporating these ICs. Parallel advances in manufacturing have allowed increasingly complex designs to be fabricated with precision and reliability.
For example, developments have been made to the gate structures of transistors in integrated circuits. At a high level, a gate structure may include a conductor and a gate dielectric that separates the conductor from a channel region of the transistor. With respect to the gate conductor, developments now allow the use of layers of metal as a substitute for polysilicon in the gate conductor. Whereas polysilicon once replaced metal as a gate conductor because of polysilicon's increased resistance to heat and ease of fabrication, metal is once again replacing polysilicon in part because of metal's higher conductance. In an example, a metal-containing gate conductor includes numerous layers including a number of work function metal layers and a low resistance metal filling layer.
With respect to the dielectric, silicon oxide is a suitable gate dielectric material in some applications. However, as a gate dielectric becomes thinner, charge carriers may tunnel through the dielectric and travel from the gate conductor to the channel region. To address this, high-k dielectrics and other gate dielectrics are being pursued that provide the same or better performance as silicon oxide with a thicker dielectric layer.